Safe discharge question about CR2 rechargeables

LogicalBeard

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I bought "SUPEREX 6 PCS of 3V 400mAh CR2 Battery 15270 15266 Rechargeable LiFePO4 Battery" off of Amazon. The description says the "End-off voltage" is 2V and that there is a "built-in safety circuit".

1.) Can anyone confirm that it is safe to discharge these to 2V?

2.) Can anyone confirm that the safety circuit is an over discharge protection circuit that shuts the battery off if one discharges accidentally below 2V?

I am used to dealing with 3.7 nominal voltage rechargeables and don't feel comfortable using these.

Thanks in advance to anyone that takes the time to help me.
 

ChrisGarrett

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I bought "SUPEREX 6 PCS of 3V 400mAh CR2 Battery 15270 15266 Rechargeable LiFePO4 Battery" off of Amazon. The description says the "End-off voltage" is 2V and that there is a "built-in safety circuit".

1.) Can anyone confirm that it is safe to discharge these to 2V?

2.) Can anyone confirm that the safety circuit is an over discharge protection circuit that shuts the battery off if one discharges accidentally below 2V?

I am used to dealing with 3.7 nominal voltage rechargeables and don't feel comfortable using these.

Thanks in advance to anyone that takes the time to help me.

Yeah, that's all I'm seeing, although it could just be a 'retelling' of the product literature.

https://www.mokeyinternational.com/item/?id=B010FMRWG2

PCB protection circuit and 2.0v, which seems normal for a 3.0v/3.2 li-ion cell.

Chris
 

LogicalBeard

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Thanks. I don't have any experience with 3V rechargeables. So 2.0v on that battery would be the equivalent of 2.5v or 2.7v on say an 18650 battery? :dedhorse: I just want to make certain I'm not misunderstanding.

Thanks again for helping me. Also, if there are some specific CR2 reachable batteries that are better vetted that you think would work better for me let me know. They just can't go over 3 volts or they will fry the circuits. I'm wanting to use them in a Aeon Mk III and it seems as long as they don't go much over 3 volts my only concern would be discharging them to low.
 

ChrisGarrett

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Thanks. I don't have any experience with 3V rechargeables. So 2.0v on that battery would be the equivalent of 2.5v or 2.7v on say an 18650 battery? :dedhorse: I just want to make certain I'm not misunderstanding.

Thanks again for helping me. Also, if there are some specific CR2 reachable batteries that are better vetted that you think would work better for me let me know. They just can't go over 3 volts or they will fry the circuits. I'm wanting to use them in a Aeon Mk III and it seems as long as they don't go much over 3 volts my only concern would be discharging them to low.

I don't know if things are linear, since we're talking two different chemistries/voltages.

LiFePO4 is a nominal 3.0v/3.2v depending on how the manufacturer does their testing, but they'll come hot off the charger at around 3.6v, much like 3.6v/3.7v cells come off at 4.2v.

Frankly, I wouldn't worry too much about the 2.0v and just charge them up at say 2.5v, or when you see the light step down.

They're small cells and you can't expect much out of them and who really knows who's making them?

They're cheap enough where you could fiddle with them and see what you see.

Chris
 
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LogicalBeard

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Exactly what I was hoping to hear. I am super grateful for the information.
 

magellan

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Great information, thanks.

One thing I've wondered about is the situation where both the flashlight and the battery have a low voltage cutoff. Many of my lights have that feature, and although I mostly have unprotected batteries, some have PCBs and are slightly longer (and sometimes don't fit in the lights). But I've sometimes wondered what happens then. For example, does one (presumably) kick in before the other, and then the other circuit just becomes a backup, etc.?
 
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ChrisGarrett

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Great information, thanks.

One thing I've wondered about is the situation where both the flashlight and the battery have a low voltage cutoff. Many of my lights have that feature, and although I mostly have unprotected batteries, some have PCBs and are slightly longer (and sometimes don't fit in the lights). But I've sometimes wondered what happens then. For example, does one (presumably) kick in before the other, and then the other circuit just becomes a backup, etc.?

Well, lights are different with their voltage cutoff and warning settings. The ZebraLights traditionally have a 2.85v cutoff, which is above the minimums of 2.75v for the S. Korean cells and 2.50v for the Japanese cells. For other lights, I don't know? Most of these lights, even going back to my first li-ion--a ZL SC600 in 2012, have some sort of step down, where the highest mode won't fire off, so that's a clue that your battery is getting low.

I've read it posted here that some of the 18650 PCB have a cutoff as low as 2.40v, but that seems a bit low to me, thinking 2.8v-2.9v would be normal. I'm pretty sure that I've gone lower than I should have and tricked the PCB on ultra low modes, but I don't recall the details. Some have said that's impossible. Just be aware and get in the habit of checking things often.

I'm not a protected cell guy. I still have my first two li-ion--EagleTac 3100s, a couple of Redilast 17670s and a couple of AW 16340s and that's it. The AWs are ready for the recycle bin, the Redilast sit in a SF 6P collecting dust and the ETs have been in the fridge for the past 3-4 years, lol.

For me, I've just trained myself to often check my cells and if I notice that I can't access a higher mode, then I use it on the lower modes until I can get home and charge things up.

I've had little 16340s run down on me and as long as I'm charging them up that day, I'll be fine, minus a few cycles off the life, but no biggie.

I guess I'm saying that running naked cells, using good chargers, in lights that don't have a low voltage cutoff isn't the 'disaster in the making' that noobs should be cautious of. Being prudent is a good thing, but frankly, who knows about the quality of those cells and has anybody vetted them? Just keep on eye on things.

Small 'CR2 type' generic cells are in use by the millions of devices. Just go to any big restaurant and look at all of the 'buzzers' they have. Still, I try and buy quality cells where I can.

Chris
 

magellan

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Thanks, Chris, lots of very useful info there and also your personal experience is helpful.

I really sorta pamper my batteries and am pretty conscientious about not working them real hard. This is despite my having gone to mostly lithium manganese types several years back, which are supposed to be pretty tolerant of hard use and even abuse.

I have some big high drain lights, like my Vinh modded Tk75vn77, Modamag Colossus, and a few others, but I rarely run them on high or turbo mode. But most of my lights are small, pocket lights using AAA, CR2, or other small batteries. I recharge batteries regularly, and rarely run them all the way down. So I feel I'm unlikely to have any serious battery issues, at least that I might cause personally.

I've also read that the better battery manufacturers run tests on their batteries, such as a two-hour, multi-amp, reverse current test, which seems pretty tough to me, but anyway, I figure if a battery can withstand things like that, anything I might do to it would be pretty trivial.
 
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Got Lumens?

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If Your light won't go to it's highest level, try a new CR2 cell(s) and see if that rechargeable(s) is preventing a high enough discharge rate to power the driver. If You know the discharge current of the light, the needed discharge "C" rating of the lower voltage cell(s) can be calculated. You may find one brand may work, while another may not. There are many formulations of battery chemistries/blends out there many times it becomes difficult finding just the right one. I see there is one that says USA 300mAh that looks good in the pics/specs 1A sustained discharge on eB_y.
 

magellan

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I bought "SUPEREX 6 PCS of 3V 400mAh CR2 Battery 15270 15266 Rechargeable LiFePO4 Battery" off of Amazon. The description says the "End-off voltage" is 2V and that there is a "built-in safety circuit".

1.) Can anyone confirm that it is safe to discharge these to 2V?

2.) Can anyone confirm that the safety circuit is an over discharge protection circuit that shuts the battery off if one discharges accidentally below 2V?

I am used to dealing with 3.7 nominal voltage rechargeables and don't feel comfortable using these.

Thanks in advance to anyone that takes the time to help me.

Another possibility for a CR2 size battery is these IMRs. I've been using them for several years in my small TnC lights (which put out 700 lumens on high, like the Extreme Micro Turbo) and they've been fine.

https://em-mgt.com/newsite/product/15270-red-eh-battery/
 
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LogicalBeard

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Thanks for the link magellan and all the good info from everyone else. The batteries seem to pull enough amps to hit the high mode and I like the protection circuit as a last ditch safety feature. However, I am still hesitant to use them for daily use and I have still been using primaries while carrying the light.
 

magellan

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You're welcome. You might want to try the IMRs in that case. The RMSK website recommends them for these little high-draw lights like the TnCs which they of course sell. And as I said they've worked out well in my lights.
 
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